There is a continuing need for simple, rapid and accurate qualitative and quantitative determinations of biologically active substances at extremely low concentrations. The purpose of such determinations can be extremely varied, however there is a particular need today for rapid determinations in doctors' offices, police stations, clinics and laboratories for determining the presence of drugs or narcotics in bodily fluids such as saliva, blood or urine. Therefore, there is a need for methods which do not require sophisticated equipment and which need not be conducted by specially skilled technicians. The classical methods of determining the presence of trace amounts of chemicals or drugs have not been satisfactory in meeting these needs. Thin layer chromatography has a number of deficiencies in that it is slow, requires a high degree of proficiency, and is subject to a wide range of interfering materials. Both gas phase chromatography and mass spectroscopy require sophisticated and expensive equipment as well as a high degree of technical skill.
The radioimmunoassay has long been used in clinical laboratories, however it has been prevented from widespread use in offices and other non-laboratory locations due to handling problems and undesirable hazards stemming from the use of radioactive materials. In addition, radioactive materials may be short lived and the separation of the bound and unbound radioactive analogs required in the assay technique is difficult and thus particularly subject to error.
In an effort to obviate these problems, dipstick assays have been developed which provide for color development when the analyte of interest is present. However, dipsticks are subject to many interferences and rarely can give more than a qualitative result.
Therefore, there remains a need for a rapid, accurate and simple diagnostic method requiring relatively unsophisticated equipment allowing for performance by unskilled personnel. In addition, to meet the requirements of convenience, reliability and simplicity, there is a need for a method which employs reagents which are storage stable, desirably under ambient conditions, and readily reconstituted to a homogeneous solution when provided dry or lyophilized. To meet these objectives, it would be desirable to have a single reagent which encompasses all of the necessary active materials for the test. However, since most assay systems for the determination of biologically active substances require the combination of two or more reagents in a liquid phase at the time of determination, it is necessary for a single reagent system to be maintained dry until used in the assay. However, in making a dry, single test reagent it is not possible to accurately and uniformly combine all of the necessary ingredients by measuring out each dry ingredient and combining them in a dry state. The accuracy and reproducibility necessary for an analytical reagent cannot be attained by such a method. Thus, at some point during the preparation of the dry formulation, some or all of the dry ingredients must be dissolved to form one or more solutions in order to achieve accurate measurement and uniform distribution. On the other hand, at the time the assay is performed, it is essential that the dissolution of the active reagents is rapid and that the active ingredients are homogeneously dispersed in order for the rate of dissolution not to become a factor in the observed measurement. Therefore, there has not heretofore been a single test reagent provided in a dry state which when activated by the addition of a liquid was substantially and instantaneously dissolved so as to allow for a reading within a short period of time.
As further background, U.S. Pat. No. 3,876,502 discloses a diagnostic test reagent formulation comprising a solid water soluble anhydrous storage stable mixture containing a reagent capable of participating in a test reaction to effect a measurable change in a test system, and a solid nitrogen containing polyoxyalkylene nonionic surfactant. U.S. Pat. No. 3,817,837 teaches a homogeneous enzyme immunoassay.